Wednesday, September 18, 2019

The Weather Outlook for the Rest of the Fall and Winter

The question many of you are asking is:  what kind of winter do we expect?

The question you should also be asking:  do such forecasts have much skill?

Well, I can give you a forecast, based on the best tools we have.  But the forecast skill is not as good as one would hope...as it always true beyond two weeks.

For the next one and a half month, probably the most skillful tool is the extended range European Center ensemble mean forecast--which projects out 46 days.  This forecast now goes out through 1 November.

The EC forecast for precipitation anomaly (difference from normal) through 1 November is for wetter than normal over most of the Northwest, with a few exceptions--well offshore and over southern Vancouver Island.


Temperature anomaly?  Slightly warmer than normal offshore, which makes sense with the BLOB still there..and warmer along the coast.  But pretty normal over most inland areas.


This forecast seems very reasonable to me.   

For the longer term, it is useful to look at the El Nino/La Nina situation.  Remember that El Nino is associated with warmer than normal sea surface temperatures (SSTs) in the central and eastern tropical Pacific.  La Nina is when the water in that area is cooler than normal.   Neutral (or La Nada) situations are when the SSTs are within .5C of normal.

Here is a plot from the NOAA Climate Prediction Center (CPC) of the sea surface temperature anomalies (again difference from normal) for some well-defined areas in the tropical Pacific (a map of the areas is found below).  The Nino3.4 area is the one most commonly discussed.  Time increases to the right. 

You can see we have gone from an El Nino period to a neutral period---with the sea surface temperatures cooling off a lot over the summer.



A wide variety of statistical and full physics models are run to predict the temperatures in the Nino3.4 area. The results of these predictions made last month suggest that we will end up slightly warmer than normal-- in other words, a neutral state.

And the most recent probabilistic prediction of the NOAA CPC folks is that a neutral situation is most probable, with a bias towards the warm side.


OK, the best bet now is that we will be in a neutral situation in the tropical Pacific. 

So what does that mean for us this winter?

The bottom line is that there is no reason to expect an anomalous winter in our area.  Starting with a warm Pacific and the modest warming associated with increasing greenhouse gases, going for modestly warmer than normal temperatures here in the Northwest (normal being the conditions of the past 30 years), seems reasonable.

No reason not to buy an annual ski pass if that is what you like to do.  No reason to expect any kind of drought situation.    Good weather this fall for prescribed burns to clean up our forests (WA DNR take notice!).

Does such a forecast have a lot of skill?  Te El Nino/La Nina connection with our weather can explain  perhaps about a third of the year to year variability of our weather.   Not as much as we would like, but still useful.





4 comments:

  1. Last time we had the BLOB we had a bad snow drought due to more or less normal precipitation but very warm winter temps. You don’t think that’s too likely this year in spite of the BLOB? I hope not!

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  2. Last time we had a neutral forecast we had quite a winter in Portland. Lots of lowland snow that stuck around for weeks at a time. Below freezing temps during the evenings and frequently during daytime hours. The city didn't handle it well, to put it mildly.

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  3. Is it still the case that large windstorms tend to occur in the Pacific NW during neutral years?

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  4. I also keep reading about the dreaded blob… In Cliff’s articles as well as others… But not a tremendous amount of attention. Because, like you… my memory was ‘that winter was horrible. Low snow pack. I skied on more rocks than snow. Any thoughts as to whether or not that blob will stick around? Go away? Get stronger?

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